<?php
class Father{

    public $a = 1;
    public function test(){
        echo $this->a;
    }
    public function __construct()
    {
        $this->a = 2;
    }


}

class Son extends Father{
   public function __construct()
   {
        parent::__construct();
   }

    public function start(){
       echo $this->a;
    }
}

$a =new Son();
$a->start();